Castles are pretty disgusting places, and this is where all that grossness goes. It's really kinda awful, so try not to go for a swim. Or, like, put it near anything you don't want to smell terrible.
Castle Sewage Pipe price in Growtopia: sells for about 30 WL, buyers pay about 5 WL (median of 180 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: BUJUR, 7NAP, KRFU, NFUU, SKYSWAB