This page of the guide to Resident Evil 3 Remake has a walkthrough for the sewers. Jill lost Nemesis by escaping to the sewers. There are a few valuable items in the sewers but you have to watch out for dangers like oversized mutant toads.
Find a way above ground
Soon after you start exploring sewers, you reach the Manager's Office where you can e.g. use a typewriter. You will also find a Sewers Map. The sewers aren't very extensive, but having a map is good.
Move on. On the way, you will come across the first door with an electronic lock. You can't do anything with them now - the lock requires a special battery.
Head south. Jill will be attacked by a giant toad. To eliminate these monsters, it is best to start a fight by using the shotgun or grenades (one of them can be found among the trash nearby). Later, you will be able to use the grenade launcher.
Always wait with shooting or throwing a grenade until the toad opens its mouth - this attack will inflict heavy damage. Don't let the toad get close - it will eat you.
We recommend reaching the Office located at the southern end of the sewers. The reason for this is that you will find an MGL Grenade Launcher. This is an excellent weapon not only for killing toads but also other powerful opponents. Search that office and you will find e.g. a note about crafting grenade launcher ammunition and a typewriter.
Return to the fork you passed earlier and head west (watch out for the toads!). Once you reach the next fork, you must choose the left tunnel.
You will reach another small ladder leading to the lab. You will find a Battery Pack - you will need it to get out of the sewers (note - batteries require 2 free inventory slots!).
Head back to the eastern part of the sewers and then head north. More toads will stand in your way. About halfway, use the longer ladder to reach the upper level.
Find a hip bag nearby - it increases inventory capacity by 2 slots. It is hidden in the security room. Getting to it is not easy because the door has an electronic lock. Here are the steps you need to take:
- Get to the locked door from Step 1. Put the battery in the lock and open the door.
- Reach the door from Step 2 and open it from the northern side.
- Return to the door from Step 1 and remove the battery from the slot (you only have one battery, which means only one electronic lock can be powered at a given time)
- Go through the open door from Step 2 and reach the closed door from Step 3. Put the battery in the slot again. You can go inside now and take the pouch.
Get out of the security room and remove the battery from the lock on the door - you will need it later. Find the ladder going to the lower level.
You have to reach the locked doors you encountered at the very beginning of your visit to the sewers. Use the batteries for the last time. Don't worry about leaving them in the lock - you won't need them anymore. Take the narrow corridors upstairs. Nemesis appears and drags Jill to the surface. Don't worry - you aren't able to avoid this attack.