I don't know if you've noticed that the Owners Manual at the link boathealer posted is the one for the RV version. At least it includes some maintenance instructions...the owners manual for the marine version--only9 pages--doesn't. In fact, it's an even more pathetic excuse for an owners manual than Jabsco's owners manuals! Tecma Silence Marine owners manual
As for joker valves...looking at the exploded drawings for both version, it doesn't appear that there is one. Both versions have only one motor. They include both the 12v and 24v pumps in the parts list 'cuz they have different part #s, which can mislead you into thinking there are two if you miss that little detail.
Is yours the fresh water or sea water version?