I have a problem at work and unfortunately it has been too long since I have been in a class room for me to reason this one out, never did like fulid mechanics much :). We have filter that is pressurized to approximately 55 psi. Once ever 12min or so this filter purges a volume of ~2L that for the sake of this problem we can call water. The facilites side of our building says that they can not accept pressurized liquids to this system. As far as I know it is an open drain line that is usually gravity drained to a waste collection barrel on the floor beneath the tool. The thought from some of my coworkers was first to add a collection tank and then gravity drain from there. Then the though was what if we just expanded the drain line to ~4" line and then reduced to tie into the facilities line (approximately 2" line). The question came up, How long of a section of 4" pipe do we need to get this 2L (55psi) volume of water down to around 10psi. I thought oh this will be easy but then I remember... well this isnt a gas so i can't use the equation I thought I was going to. I don't have constant flow in the pipe either so Bournoulli's gets a little weird as well. Is this event the right way to think about fixing our pressure problem? If so, any help on how I can calcuate how long of a section of 4" pipe we need to install to reduce our water pressure to the desired 10psi?