I recently purchased a 2013 Heartland Prowler 32P BHS on a seasonal site. According to specs I have read online the trailer has 1 fresh water tank, 1 grey water tank and 1 blackwater tank. The drain for the grey tank and the drain for the black tank flow into a single connection under the trailer between the slides at the rear of the tires. There is an individual tank valve drain handle on each side of this common sewer connection and it flows into a septic tank. Now, under the rear of the trailer there is a another drain pipe with a valve at the end of it. This pipe comes out of the lining under the trailer and drops at a slight angle and has a cap on the end. It is not connected to the septic tank. I cannot find anything that tells me what this pipe is for. What is it? And, should it be linked to the other drain/s and run into the septic? It's also getting close to winterizing time and I also need to know if I should open this drain to ensure there is nothing in the pipe. The pipe is about 3 to 4 feet long.