During your visit to Saturn Valley, a Mr. Saturn told you the password to enter Belch Base.
Enter Belch Base
Now that you know the secret of getting into the Belch Base, go back through the short cave and go north to the waterfall. The Photo Man will take your picture as you approach. Step through the falling water and walk left, then when you can't go any farther left, try to go north. The guard will ask for the password. Don't push any buttons. The dialog box will eventually go away. After three minutes of waiting, the guard will say "you may enter," and you will automatically go into the base.
Go through Belch Base
If you don't have the Jar of Fly Honey, you will have to leave and get it, then come back after you have it.
The Foppys in this area will attack in swarms, but they are easy to defeat, and they give a lot of Exp.
The Slimy Little Piles are vulnerable to Paralysis.
From the entrance, go to the right. Go through the door on the right and check the trash can to get a Bomb. Then leave the room and go down the ladder.
Go west, then south down the ladder. Go into the room at the bottom and check on the trash cans to get an IQ Capsule and Broken Laser. Then leave the room and go up the ladder.
Go west, past the conveyor belt area. Go up the ladder and enter the room there to get a Vital Capsule, HP-Sucker, and Calorie Stick. Then leave the room and go back down the ladder.
Go west. You can enter the room here to find a Magic Butterfly. If it's not there, just leave and go back in. Use this to heal up.
From the Magic Butterfly room, go west and fight the Slimy Little Pile that harasses you, then go through the door at the end. Then go to the left and talk to Master Belch to fight him.
Defeat Master Belch
The Jar of Fly Honey makes this battle easy. If you want an extra challenge, then don't use the fly honey. However, if you do this, then the only way to damage Master Belch (unless you are playing an older version of the game) is to use the HP-Sucker. Alternatively, Paula has to pray until Belch feels strange, and then he has to inflict Nausea on himself. These strategies take a long time.
The easy way to defeat Master Belch is to use the fly honey on him. After using the fly honey on Master Belch, he almost never attacks. If he inflicts nausea on anybody, use Healing β or a Refreshing Herb.
If you want to end the battle quickly, just use Bottle Rockets and Ness and Paula's best PSI. Or you can just take your time and use physical attacks. Belch is highly vulnerable to sleep, but it's hardly necessary if he's eating the fly honey.
When you get rid of Master Belch, you can go through the door behind him to return to Saturn Valley. There, you will be able to reach Milky Well.