1. When it is convenient to you, I'll visit you at 6.

Question

(In this sentence, what does 'it' refer to?)

2. He paid all the debts by automatic deposit.

3. The baby peed/weed on the diaper too much.

4. You should teach the baby to give out dung in the bathroom alone without using a diaper step by step.

(Would you correct any errors in the sentences above?)

Answer 1

1. When it is convenient to you, I'll visit you at 6.
This doesn't make sense with a specific time included. Use one or the other of the following:

When it is convenient for you, I'll visit.
or
I'll visit you at 6 pm tomorrow.

(In this sentence, what does 'it' refer to?)
This is one of those instances in which "it" doesn't refer to anything in particular. Weird, right?
2. He paid all the debts by automatic deposit.

3. The baby peed on the diaper too much.

4. You should potty-train the baby, step by step, starting about age 2. Teach each him to use the bathroom and gradually stop needing diapers.