Overloading septic

david_caryJuly 30, 2011

I am building a house that is a vacation rental and by necessity, it will be occasionally filled with more people than the septic system is designed for. I am trying to find out what I can do to minimize the problem. It has a 4 bedroom septic but may be filled with 12-14 people and it is very hard to control what short term renters will do.

I was going to go with 1.3 gallon toilets and of course code compliant shower heads. There will be only 1 bath tub.

One thought was to run the shower and bathroom sink drains separately and use that for gray water irrigation (if allowed). But I've heard that you need some amount of "clean" water for everything to function correctly. Certainly some of the water could go to septic and some to irrigation.

Obviously no garbage disposal. Frequent cleaning out (annually?). This is an area with a 12 week peak season so it won't be filled a lot of the time.

Any thoughts/advice?

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i'd eliminate the tub and install an outside shower as well--assuming you are on a lake or some such.
add a dishwasher too and maybe no laundry facilities.
hopefully there will be enough time between large parties for it all to be absorbed.

    Bookmark   July 31, 2011 at 9:44AM
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There will be an outdoor shower. Laundry facilities are mandatory.

We need the tub - I feel like you have to have one for the little ones.

After some more research I am thinking of 2 cleanings in the summer months. So there would be 4 weeks with crowds, a cleanout, 4 more weeks, cleanout, and then finish out 4 more weeks.

The soil is great (ie percs well) but the municipality won't allow anything larger. There is a repair field but I hate to have to use it anytime soon.

If it is just a volume of water issue, then the greywater solution should work well. I can do frontloader washer and an ES dishwasher. I guess I can hope that people on vacation might tend to be constipated....

    Bookmark   July 31, 2011 at 3:41PM
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"If it is just a volume of water issue..."

That is the main problem.

The drain field can become saturated, and solids can be carried out of the tank into the field wrecking it.

    Bookmark   July 31, 2011 at 3:45PM
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Can you install two drain fields and switch back and forth? Also, make sure you have a filter on your septic tank.

It is highly unlikely any municipality will allow you to use your gray water for irrigation, but I guess it never hurts to ask.

    Bookmark   July 31, 2011 at 3:57PM
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Actually a lot of municipality's allow graywater for irrigation. It is pretty universal in the SW. It is allowed in our state, just up to local jurisdictions to control. 2 drain fields is not an option.

I believe filters are code now.

    Bookmark   July 31, 2011 at 7:44PM
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The design is normally specified as a minimum size tank and a minimum length and depth of drain field to accommodate the design. The county should not care if you put in a larger tank, add a couple feet of depth and extra 20 feet of length to the field. At inspection they should be looking to make sure you meet the minimums in the design. Ask the inspector to verify this.

Note that if you dig the field 20 % larger but only put in the required amount of pipe that should suffice. I have never had an inspector complain about having over built to the specification. They are usually limiting the design to stop you from remodeling without a need to return for extra fees and to limit year around permanent occupancy.

If you only use the house during part of the year, mainly in the summer when water table is at its lowest the odds are the problems will be limited.

Make sure all cleaning supplies are in the house and avoid Chlorine and bleach. They kill the bacteria in the septic system. You should add live bacteria to the system between and before the tenants to improve activity.

You should install an accessible cleanable basket filter in front of the drain field and make sure you have a riser with a lockable manhole access to facilitate pumping and servicing. The filter will catch condoms, tampons, sanitary napkins, bone pieces and things people are not supposed to put down the system. These will clog the drain field pipes if you do not put in the filter. This is a common problem for rentals. I have had this problem.

Note that if you put in a gray water system that you should make sure you have easy access to a clean out in the toilet lines. Having at least one sink in the line before the drain line gets to the toilets is also a good idea to assist flushing the solids to the tank and cleaning if needed. Normally you design plumbing flow so that the sinks and showers are uphill in the plumbing to assist flushing. This is not required but is part of good design. All of the above should be part of the design if the septic designer and plumber are any good. These are often skipped by installers that are low bidders. Make sure your specification for quoting includes these features in the design.

I have been building net zero, passively heated, utility free homes for the same cost as a standard custom home since the 70s. If you need some additional help you can contact me at zehboss@gmail.com.


Here is a link that might be useful: OH INC. home of Holistic Integrated Design using Engineered Natural Systems

    Bookmark   August 13, 2011 at 5:02AM
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Helpful info Brian.

The fields are staked already and there is no room to increase the size. There is no room to grow the tank any either. I am pretty sure the filter is code but I do need to make sure that it is easily accessible.

It sounds like for gray water, you are referring to something to use to flush the toilets. While that is better (ie less water use), my priority is minimizing septic. Rainwater is plentiful and that would be my plan if water use reduction was my goal (not that it isn't, but it just isn't primary right now). I probably am getting better return on solar. The main reason to use rain water to flush the toilets is that it makes so much sense but it really is hard to justify on a $$ basis

    Bookmark   August 13, 2011 at 6:08AM
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