That definitely looks like the tank fitting...first time I've seen Dometic (formerly SeaLand) fittings in any color but white. Replacing the gooed up one will be a lot easier than trying to remove the goo.
If you're handy with a hole saw you can make a pumpout diptube for a fraction of Dometic's price...All you need is a 1.5" Uniseal UNISEAL
and a piece of sched 80 pvc pipe (available from the plumbing dept in any big box store) that has a 1.5" OD (outer diameter) to fit inside 1.5" hose cut long enough to touch the bottom of the tank plus about 4" above the top of the tank. You'll cut the bottom of the pipe at about a 25 degree angle (any flatter can trap TP under it, any sharper leaves too much in the tank)...the extra 4" at the top becomes the pumpout hose connector. I'll be glad to provide more detailed instructions if you'd like to send me a PM.
Raritan SaniFlex is the top rated hose...a great choice. And btw, replacing hoses doesn't have to be messy stinky job These instructions should have been included in the current edition of my book but were omitted:
Before you begin, flush a LOT of clean fresh water through the entire system including the tank.
Start with the highest connections, duct tape or plug the ends as you remove each one.
Warming the old hoses a bit (I always used a blow dryer) will make them easier to get off the fittings.
Put a plastic waste basket liner under each connection to catch any spills.
Warming the hose also makes it easier to get the new hose onto the fittings. Lubricate the inside of the hose and the outside of the fitting with a little K-Y...it's a water soluble surgical jelly that dries out and is also much slipperier than dishwashing liquid.
And I'm sure you already know that all hose connections should be double clamped, with screws 180 degrees apart...or at least 90 degrees if access makes 180 impossible.