There are several mentions of unions and yes - place them with a shut off valve nearby so you can dismantle the plumbing for maintenance when needed. You have a center flow on the tank, mine is similar - I have a 90 gallon. I used a 20g long for the filter. Basically I have 2 drainpipes from the tank into a filter bag, and 1 return from the pump. to the tank I created a manifold and "T" off 2 fittings to the tank. There was a video posted, and my setup is very similar to that. It appears from your picture that your tank is located at the bottom of stairs. Mine is as well, I cut an access panel in the wall behind the tank and put all the filtration and electrical thru the access into the area under the stairs. I have room under the tank for supplies. One other point to mention is that I placed my filter and pump on 2x4's and created a platform about 4" above the floor, this enabled me to keep everything level and off the floor away from any spilled water. Good luck!