If it were mine and I saw what is in the picture, I'd remove the plug at the right end of the brass right angle and get your water pressure there. Thread sealant sometimes is applied to OEM manufacturing parts to speed up assembly. Teflon tape would work fine on your installation.
Seems that the flush designer had the forethought to allow an additional use for the port that is usually used for water pressure and/or temperature....give him/her an atta boy/girl on that one. I have a temp "kit" in my 2002 115, plumbed from the same port. I really like it, my first after many years of boating. I bought the boat used last year and water pressure seemed to be more than adequate so I didn't want to tear into the LU just to be doing it......to each his own here. My boat had 3 large circles in the dash with one tach, one the speedo, and the other blank...probably a spin off from the old original circular flasher depth finder. I said hmmmmmm what would be useful there.
I don't know what happened to the edit to my reply......went poof See if I can say what I said: A pressure gauge may be a better installation for you in tapping into the Brass fitting. Reason being you won't be plugging the port with a thermal sending unit....probably would upset the functioning oft he flush with reduced volume capability through the port. On an alternative location for the temp sender, that's a lot of trouble. Pressure is preferred by lots of folks that work this forum, especially Bassers and Offshore folks.
