I had someone finish my basement and add a full bathroom in it. He had to install a pump to which the bathroom water goes to. This pump smells weird. At first the smell wasnt too strong but about 2 months later its terrible! I rented out the basement and the tenant had to keep that window open to tolerate the smell (the pump is located in the boiler room with is next to the small living room in the basement). My brother has cleaned this thing with bleach and nothing seems to work. I read about putting silicone around the top and sealing this thing but is this safe to do? would it open in case it gets clogged or something? do I also seal the area where the cables come out of? I tried covering it with a comforter but it still smells in the apartment and I am trying to get this fixed before renting it out again because the first thing the ppl will get hit with is that smell, which will make them want to run... Help!!!

you need to be sure of where the smell is coming from so that you fix it right the first time.
do not silicone the cover down.
you can remove the cover, lay down a good amount of silicone around where the gasket should seal the cover. put some saran wrap over the still wet silicone and attach the cover. this will make a good seal but the cover is still removable.
a tiny amount of silicoe where the wires stick thru the grommets won't hurt anything.
post a photo so we can have a look-see. maybe we can see something you can't..
BTW, the smell is normal. horrendous but normal. but it must be contained within the tank and should travel up the vent when you flush the toilet.

"Someone finished your basement... and added a pump"

Was the work inspected by the town/city? Sorry, but I had to ask as it could all go back to the original install and if it was done properly. Best Efforts, may go a long way to complete a plumbing job, but if it wasn't done right.......
And if you are renting out the space, you are potentially looking at some future responsibilities. I'd consider bring in a licensed plumber to inspect the installation first.

Best Wishes

Did they install a vent so your ordors have somewhere to go?...

any open space around the plumbing pipes and the electric pump wire need to be sealed air tight with silicon. The waist container vent plumbing joints need to be sealed and vent opening should be unrestricted. P trap of shower area, sink if not maintaining water seal will let the foul smell spread in the basement.