One suggestion I have is to have a a bucket (the 5 gallon Home Depot type buckets are usually too tall, but a cleaning bucket from the grocery store works), and put the bucket down below the output when pulling the cap off. I am glad we had this when we first bought our 5th wheel as we had an issue with a secondary valve being left open (we didn't know we had two, oops,was thankfully just gray water) and the water started coming out out in a big hurry. The bucket collected most of it while we got the hose on and over to the cleanout. Even with valves closed we usually have a bit of drippage, so it's nice to collect it in the bucket, instead of on the ground.
