Hello again, I installed the faucet with the rubber washer underneath the counter. When I turned on the faucet there was water leaking from the supply lines where they connect into the base of the faucet. The supply lines were preconnected by the manufacturer so I cannot access to tighten them inside the base of the faucet. Should I just disconnect and return the faucet or is there a possible fix?

This is why one hires a plumber. You’re asking for help, without ever mentioning what brand and model the faucet is.

The faucet is a moen faucet torrance low arc single handle faucet.

I am sure I am not the only who has attempted to install a kitchen faucet. It is not something that necessarily requires a plumber to install. However asking a couple of questions is reasonable as many others do on this forum.

Hi Jen - I am in process of installing bathroom faucet. I believe the rubber washer goes underneath the counter just like you installed - rubber washer goes first then the metal washer. When you say water is leaking, are you sure it is leaking close to the faucet and not the supply line nut?

The faucet is installed as pictured. When you tighten the screws into the last washer, the base won't move.

Let's see a picture of the supply lines connecting to the faucet please.