What is a Floor Drain?

A floor drain consists of the drain body set into the floor slab, a grate on top, often a removable sludge bucket, and the trap. Below it, the pipe leads into the underground drain and on to the sewer.

The trap is a small reservoir of water that blocks sewer gases. The product standard DIN EN 1253-1 covers floor drains with a trap seal depth of at least 50 mm. The problem in a basement: many drains get no water for months. The seal evaporates, and it smells of sewer. A bucket of water at regular intervals keeps the trap filled.

Old basements often have cast-iron drains with no backflow protection at all. They drain water reliably, but during backflow they let it in just as reliably.

A floor drain in the basement is an open connection to the sewer. When the water level there rises, for example because heavy rain overloads the combined sewer, it pushes up through the underground drain. How high this can go is described by the backflow level. The municipality sets it; where it hasn’t, DIN 1986-100 uses the top of the road at the connection point. Every drain below that is at risk during sewer backflow.

What comes out is not rainwater but sewage from the sewer. That is why municipal drainage bylaws oblige owners to protect drains below the backflow level. According to the German consumer advice centre (Verbraucherzentrale), owners who don’t are liable for backflow damage themselves.

• Sewer smell: the trap has dried out. Top it up with water.
• Water drains slowly: sludge bucket full or flaps dirty. Lift the grate, empty the bucket, clear hair and lint from the flaps.
• Flap doesn’t close: dirt or limescale on the seal. During backflow, sewage then ends up in the basement anyway.
• Emergency closure left shut: your own water can’t drain either, for example from the washing machine.

For backflow valves, operator rules based on DIN 1986-3 say: operate the emergency closure once a month to check that it works. According to the German federal flood protection guide, servicing by a qualified person is required every six months; Kessel and other manufacturers state the intervals in their manuals. Servicing means cleaning the flaps, checking the seals and testing for tightness. It is also an insurance issue: according to the Verbraucherzentrale, if you don’t have backflow protection checked and serviced, you risk your insurance cover.

You need a professional if an old drain without backflow protection is to be retrofitted, if it isn’t clear where the backflow level is, or if a flap is damaged.

To be honest: a floor drain is not a place for Drainbee. The probe needs a shaft with standing water, i.e. a pump sump or lifting station. Drainbee does not see backflow pushing up through a floor drain. If you want a warning there, put a water leak detector right in front of the drain.

If your basement also has a pump sump or lifting station, that is where Drainbee measures the level and raises an alarm on threshold, power outage or WLAN loss.