Review on EasyDrain 510 Expandable Flexible P Trap by Teo Alston

. Check valves allow water to flow normally down the drain, but when something tries to back up and move up the pipe, the valve closes (and seals tight). We don't need non-return valves upstairs, but they are indispensable in the basement. If you install a check valve under the sink in the bathroom in the basement, you will have very little closet space. Check valves when adjusted by glue adapters to go from the larger 1 1/2" pipe that the check valve requires to the 1 1/2" size that these flexible drain pipes are made for them quite long. Two of these flexible drain hoses work fine (one at each end of the check valve). I attached a pre-built up and down check valve with two flexible drain pipes to a corner cabinet under the sink in our basement bathroom. Be careful not to install the check valve upside down! (Check valves have an arrow showing which way water can flow).