Don't know if your trailer is similar to mine, but I have 4 "low point drains". Two are under the vanity in the bathroom and are connected to the pressurized water system. If there is city water connected or the pump is on (and there's water in the fresh tank), these valves will shoot out pressurized water when opened, just like any other faucet in the system. They are T-valves and are pulled up to release. The O-rings on these valves are problematic.
The other two are gravity drains for my fresh water tank. The fresh water tank is not pressurized, and the valves are the 1/2-turn variety. I have 80 gallons of fresh capacity, and when those tanks are full, it takes FOREVER to drain through those little valves.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!