How can we get out of a lease due to plumbing problems?

You need to send the landlord a letter detailing the problems, requesting that the problems that they be fixed within the next two weeks, and keep a copy of that letter for yourself. If the landlord fails to commence repairs during that time, then you have a right to terminate the lease and move out. You also have the option to make repairs if the landlord fails to do so, at a cost not exceeding one months rent every six months. You may also wish to consider contacting the health department to perform an inspection. Ideally, you take pictures of the problem the next time it occurs, so that you could provide copies as appropriate in the future.

This is a health and safety issue and will allow you to withhold rent while the problem persists. If the landlord does not take action within a reasonable time you may also pay a plumber to fix the issues and deduct the payments from your rent. These issues go to habitability and this is a defense against an unlawful detainer for non-payment.

Depending on your lease, or rental agreement, it would appear that the house is actually uninhabitable and the condition must be either corrected by the landlord or you may be able to claim that you have been constructively evicted. Another place to bring your concerns is the local health department. Be careful, as if you do not do this correctly you potentially will be liable for continuing rent or the remainder of the funds due under the lease.