The way those taps work is the main circuit is protected by original fuse so say 20A then you can put whatever different fuse in the slave part but I wouldn't want to overtax the original circuit.
Try Musology Auto they have everything you need. They have a page or 2 on the forum also.
https://www.amazon.com/stores/Muslogy/page/3C2C74A8-30A1-4B3B-B623-5CF01FE0A864
You can use those for draining if you have a tonneau cover and the white piece has been discussed many times some take it out others leave it. It does cover one of the cab vents but doesn't impede the air flow. Me I just left mine doesn't hurt anything.