Summer Drain Prep: Protecting Your Building During Extended Closures

Every June, thousands of schools, universities, and seasonal businesses close their doors for weeks or months at a time. The lights go off, the HVAC systems cycle down, and the building sits empty. What most facility managers do not realize is that within two to three weeks of closure, every floor drain in the building begins losing its trap seal to evaporation. By the time staff return in August or September, the building smells like sewer gas, drain flies have colonized restrooms, and the indoor environment requires days of remediation before it is safe for occupants.

This does not have to happen. With proper pre-closure preparation, you can protect every drain in the building for the entire duration of the shutdown. This article provides a practical, step-by-step guide for facility managers preparing buildings for extended summer closures.

Why summer closures are dangerous for drains

The P-trap under every floor drain holds a small pool of water that blocks sewer gas from entering the building. This water seal works perfectly as long as the water is replenished through regular drain use. During a building closure, nobody is using the drains. Nobody is running water. The water in the trap begins evaporating from day one.

Several factors accelerate evaporation during summer closures:

• Higher ambient temperatures increase evaporation rates significantly. A drain that holds its seal for 3 weeks at 68 degrees may lose it in 10 days at 85 degrees.
• HVAC systems running in dehumidification mode pull moisture from the air, including from trap water. Even reduced-capacity summer HVAC settings accelerate trap dry-out.
• Air movement from ventilation across the drain opening acts like wind over a puddle, speeding evaporation.
• Low humidity in arid climates creates a larger vapor pressure differential, causing water to evaporate faster.

Which drains dry out first

Not all drains lose their seal at the same rate. Understanding which drains are most vulnerable allows you to prioritize your pre-closure efforts.

Highest risk: drains in conditioned or ventilated spaces

Floor drains in spaces where air moves across the drain opening dry out fastest. This includes mechanical rooms with exhaust fans, corridors with air handling systems, and any space where the HVAC system continues to operate during closure. These drains can lose their seal in 7 to 10 days.

High risk: drains near heat sources

Drains near boilers, water heaters, steam pipes, or server rooms experience elevated temperatures that accelerate evaporation. In a mechanical room that stays at 90 degrees through the summer, a trap may dry out in under a week.

Moderate risk: restroom floor drains

Restrooms that are not used during closure lose their floor drain seals within 2 to 4 weeks. Toilet and sink traps are usually protected because they hold more water, but floor drains in restrooms have smaller traps and dry out faster. These are often the drains that produce the sewage smell people notice on the first day back.

Lower risk (but still vulnerable): enclosed, humid spaces

Drains in janitor closets, basement storage rooms, and other enclosed spaces with minimal air movement dry out more slowly. However, during an 8- to 12-week closure, even these drains will lose their seal. Do not assume any drain is safe during an extended closure.

Pre-closure checklist for facility managers

Complete this checklist before the last day of occupancy. Doing this work proactively costs a fraction of the remediation effort required after traps have failed.

Step 1: Create a complete drain inventory

Walk every floor of the building and document every floor drain, including drains in spaces you rarely visit. Include mechanical rooms, janitor closets, storage areas, elevator pits, stairwell landings, locker rooms, kitchen prep areas, and loading docks. Many buildings have drains that have not been on anyone's maintenance list for years. Your inventory should include:

• Drain location (building, floor, room number)
• Drain size (2", 3", 4", or 6")
• Last known use date
• Whether the drain has a trap primer installed
• Current condition (flowing, slow, blocked, dry)

Step 2: Flush every drain

On the last day before closure, pour at least one gallon of water down every floor drain in the building. This fully charges the trap and starts the clock. For a typical P-trap, this buys you 2 to 3 weeks before the seal begins to fail.

Step 3: Check trap primers

If your building has trap primers installed, verify that each one is operating correctly. Listen for the periodic discharge of water. Check for mineral deposits or valve failures. A trap primer that is not functioning provides zero protection during closure. Many facilities discover their trap primers failed months or years ago without anyone noticing.

Step 4: Assess closure duration against trap life

If your closure is 2 weeks or less, a single pre-closure flush may be sufficient for most drains. If your closure is 3 weeks or longer, you need one of two strategies: scheduled flushing visits during closure, or permanent waterless trap seals.

Step 5: Choose your protection strategy

You have two options for closures longer than 3 weeks:

Protection Strategy Comparison
Manual flushing vs. waterless trap seals for extended closures
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Option A: Scheduled flushing during closure

Assign a staff member or contractor to visit the building every 2 to 3 weeks and pour water down every floor drain. This is the traditional approach, and it works as long as the schedule is maintained perfectly.

Practical challenges with this approach:

• Labor cost: For a large school campus or university with hundreds of drains across multiple buildings, each flushing visit can take a full day or more.
• Consistency: Vacations, sick days, and staff turnover during summer months can cause missed visits. One missed visit is all it takes.
• Completeness: Every drain must be flushed every visit. Drains in locked rooms, behind equipment, or in hard-to-access locations are frequently skipped.
• No verification: There is no way to confirm a drain was actually flushed without physically inspecting each trap.

Option B: Waterless trap seals

Install a waterless trap seal in every floor drain before closure. The seal creates a physical barrier that blocks sewer gas, pests, and pathogens regardless of whether water is present in the trap. The building can remain closed for any duration without drain-related issues.

Advantages for seasonal closures:

• Install once before closure: No return visits required during the entire shutdown period.
• No labor cost during closure: The seals work unattended for weeks, months, or years.
• Protection starts immediately: Each drain is sealed the moment the device is installed.
• Year-round benefit: The seals continue working after the building reopens, protecting low-use drains that rarely get flushed even during normal occupancy.

Use our Water Savings Calculator to compare the annual cost of manual flushing or trap primers against a one-time waterless seal installation.

Building types most affected by seasonal closures

K-12 schools

Schools are the most affected building type. Summer breaks of 8 to 12 weeks guarantee complete trap dry-out in every floor drain. The consequences are well known to school facility staff: sewer gas odor on the first day back, drain fly infestations in restrooms, and complaints from teachers and parents about indoor air quality. Some districts spend the first week of pre-planning remediating drain issues instead of preparing classrooms.

Universities

University campuses face the same challenge at larger scale. Dormitory buildings, lecture halls, laboratory buildings, and athletic facilities all have floor drains that sit unused during summer. The problem compounds because university campuses often have hundreds of buildings spanning decades of construction, with inconsistent drain documentation and maintenance histories.

Seasonal businesses

Ski resorts, summer camps (during winter), seasonal restaurants, and vacation rental properties all experience extended closures. Unlike schools, these businesses often lack dedicated facility management staff, making scheduled flushing visits even less reliable. Facilities that close during colder months face additional challenges from freezing temperatures, which can crack P-traps and supply lines. For guidance on cold-weather shutdowns, see our article on preventing freeze and dry-trap damage during winter building closures.

Commercial buildings with seasonal vacancy

Office buildings with high vacancy rates and retail spaces between tenants experience the same dynamics. A vacant tenant space with floor drains can produce sewer gas that affects adjacent occupied spaces, creating complaints and potential liability.

What to do when you return

If you did not protect your drains before closure, here is what to do on day one:

1. Open exterior doors and windows to ventilate the building before occupants arrive.
2. Walk the building and identify dry traps by smell. Sewer gas has a distinctive rotten-egg odor.
3. Flush every floor drain with at least one gallon of water immediately.
4. Check for drain fly activity. Look for small moth-like flies near drains, especially in restrooms. Drain flies indicate traps have been dry long enough for breeding colonies to establish.
5. Allow ventilation for 24 to 48 hours before full occupancy if sewer gas exposure has been significant.
6. Document which drains were dry so you can prioritize them for waterless seal installation before the next closure.

Frequently asked questions

How do I prepare drains for summer closure?

Before closing a building for summer, create a complete drain inventory and flush every P-trap with water. Prioritize drains in low-use areas like mechanical rooms, storage closets, and unused restrooms. For closures longer than 2-3 weeks, schedule periodic flushing visits or install waterless trap seals that maintain the seal without water. Check trap primers for proper operation and verify all floor drains are accessible.

Which drains dry out fastest?

Floor drains in HVAC-conditioned spaces dry out fastest because moving air accelerates evaporation. Drains near heating equipment, in mechanical rooms with ventilation, and in areas with low humidity can lose their trap seal in as little as one week. Drains in enclosed, humid spaces like janitor closets tend to last longer, but still dry out within 3-4 weeks in most climates.

Should I hire someone to flush drains during summer?

If you are relying on water-based P-traps, yes. Someone needs to visit the building every 2-3 weeks and pour water down every floor drain. For a large school or university campus, this represents significant labor hours across hundreds of drains in multiple buildings. Many districts find that installing waterless trap seals before closure is more cost-effective than paying for repeated flushing visits.

What is the cheapest way to protect drains during building closure?

The cheapest short-term option is to pour water down every drain before closing and schedule flushing visits every 2-3 weeks. The cheapest long-term option is to install waterless trap seals, which cost a one-time fee per drain and require no ongoing labor, water, or maintenance during closures. For buildings that close annually, waterless seals typically pay for themselves within the first year through eliminated labor costs.