I don't quite follow your description, the standpipe configuration might be part of the problem. The gurgling toilet indicates a venting problem, I don't think it would contribute to overflowing, but it is a problem. As mentioned, a photo or diagram is needed for better assessment. My intent is to describe a proper washer installation and address how the height plays into it.
There are all sorts of variations for pipe configurations, this one is very typical. The washer drain ties into the 4" horizontal pipe with a vertical 4x4x2 LTTY (long turn tee-wye). It can be installed flat to gain some vertical, at the cost of an extra ell that introduces a potential clog point.
From the LTTY is a vertical 2" pipe as short as possible before connecting to a 2" sanitary tee. A 2" vertical pipe continues up to tie into the venting system. The vent could be reduced to 1.5" if need be. The side inlet of the santee takes a 2" horizontal (2% slope actually) trap arm. There is a length limit, but it's rather long, it's best to keep it rather short. The trap arm connects to a 2" trap assembly. The trap inlet accepts a 2" vertical stand pipe.
The stand pipe must be a minimum 18" high, straight up, no bends. You cannot connect a washer discharge directly to a closed drain system. There must be an overflow provision such as an open stand pipe. I prefer to see about a 24" stand pipe, but 18" is a code requirement.
This gives you about a 24-30 inch tall stand pipe/trap assembly on top of the 48" height of the main drain, so a total 6-6.5 feet off the floor. Washers have a limit of how high they can pump discharge water. The installation instructions should tell you this somewhere. If not, you may need to contact the manufacturer. If your washer can pump up to the top of the stand pipe while sitting on the floor, you're all set. If not, you will need a platform that raises the washer to within the allowable discharge height.
If you still get overflowing with a proper standpipe-trap configuration, then the main line remains obstructed somewhere.
I realize that this response is about 3.5 years after your original post was published, but I thought I would add my knowledge/experience to possibly help the next guy.
I to live in Ohio (southwest) in a house built in 1963, and I believe I have the same set up as you. I also just had a backup after a hard rain.
All of the following information is specific to my house, but I believe it will be applicable to you. The pipes coming into the pit are from the foundation drainage system around the house. The foundation drainage system directs rain water to this pit. The drain at the bottom of the pit connects directly to the main sewer line of the house. The main sewer line of the house is connected to the city sewer.
In a perfect world all rain water around the foundation of the house would gather in this pit, then drain to the city sewer. This arrangement is not much different than modern setups, it just does not have a sump pump because the house is high enough to use gravity to drain to the city sewer.
In a unperfect world your house main sewer line could be partially plugged with roots (this was my problem). When your house main sewer line is partially clogged and there is a hard rain, the discharge of the pipe simply cannot keep up with the new rain water coming in. This is what caused my back up. Being that the pit drain is connected to the house sewer line, that explains how organic matter makes its way into the pit during a backup (rain water and sewer using the same pipe).
At my house, I would not call the drain at the bottom of the pit a “whole house trap”. Rather just a trap connecting foundation rain water system to the sewer line.
I have the same drain in your photo. There is a ball in my drain. The ball is supposed to act as a one-way check valve. I was able to snake my drain out by pushing the ball to the side and by using a very small snake. I should add, the ball in my drain was stuck and needed to be forcibly dislodged before I could snake. Before I snaked my pit drain I used to have standing water as well. After dislodging the ball and snaking, I no longer have standing water in the pit.
Hopes this helps someone understand an old house system in the future. Thanks
Best Answer
Regulations (if any - they are mostly concerned with minimum sizes) will vary with the LAHJ (local area having jurisdiction) but the simple and practical consideration (if connecting to a sewer) is that your pipe size from the house should be equal to or smaller than the pipe size from the street.
A reduction in size will be more prone to clogging, and it's your house that will have the clog, not the general public.
There is no real benefit to the public system in limiting the size of pipe in houses - the size of pipe does not materially affect the amount of flow, which is based on number of occupants and fixtures, not the size of the pipe.
Where there is no sewer, the input connection on your septic tank will set the maximum practical pipe size (typically 4" in the US unless special-ordering a larger intake, which is really not called for on any normal-scale single-dwelling septic system.)