Sioux Chief makes a side outlet shower drain that will allow minimal removal of floor joist to make that application work. It's a special order item. word

The codes provide us a table that lists all the different types of fixtures that can be attached to the drainage system and each fixture is assigned a DFU (Drainage Fixture Unit) value. We begin listing all the fixtures and their corresponding DFU value to find the Total DFU load for the structure. Once we have the total DFU load we then consult another table that lists the maximum number of DFU's that can be conveyed by each size of pipe. By example let us consider a few fixtures: Lavatory................... 1DFU Tub/shower................. 3DFU Watercloset Watercloset >1.6gpf........ 4DFU Shower stall............... 2DFU Kitchen sink............... 2DFU Kitchen sink w/disposal.... 2DFU Kitchen sink w/Dishwasher.. 2DFU Clothes washer standpipe... 2DFU Laundry Tub.................2DFU Laundry Group.............. 3DFU Floor drain................ 0DFU As you can see if you have a standard bathroom group, lavatory, tub/shower & watercloset we can use the Bathroom Group value but if you have extras such as two lavatories, watercloset, tub and separate shower or perhaps a bidet we must then use the value of each individual fixture to compute the bathroom group. We would then use the total DFU value for the whole structure to determine the size of the "House Sewer line" (line from the structure to the septic tank or municipal main. WE must then go back to each bathroom, Kitchen and laundry ad compute the total DFU value for that room to determine the proper size of the branch lines. As these branch lines connect together we must compute the combined load of the lines connecting to determine the size of the line downstream from that intersection. The codes then give us a table listing the Maximum DFU load that can be conveyed by each size of pipe. Example; ..........................Horizontal........Vertical 1-1/4".................... 1DFU ............. 1DFU 1-1/2".................... 3 .................4 2"........................ 6 ............... 10 2.5" .................... 12 ................20 3" ...................... 20 ............... 48 4" ...................... 160 ............. 240 The code has some exceptions to this rule by example, while a watercloset is rated at 3 or 4DFU which could be conveyed by a 2" line however we must also consider that a watercloset is expected to convey solid fecal matter therefore the code requires a watercloset to be set on a 3" or 4" line. Contrary to popular belief an oversize line will clog much faster than an undersized line. When a drain line is properly sized in this manner the line will only be 1/2 full under full load which provides a sufficient liquid level to convey any solids that may be present in the waste. In order to insure proper velocity of flow this keeps the upper half of the line open for the free transfer of vent air. If a line is oversized it results in the level of liquid being much lower. In many cases the level of liquid is then not sufficient to properly suspend the solids and the solids will rub and scuff on the bottom of the pipe dramatically reducing the velocity of flow. This also allows the liquids to then seep past the solids and continue down the line leaving deposits of the solids in the line. Once the liquid has passed the solids will then begin to dry in place creating a small dam for the next cycle until the solids build up and totally clog the line.

Most things built in 1975 aren’t what they used to be. Life happens. No builder has a 42 year warranty. You’re lucky if they have a 2 year warranty.

Cat_ky, I will probably do that eventually. I don't know how they'll look into this other than cutting into the ceiling below--unless they can see what they need to see by removing that gasket. I just did some measuring, and it actually looks like my shower straddles my laundry room and garage. The drain is probably right above a wall. I might try asking my neighbors via Nextdoor if their drains appear the same. The part that really concerns me is the top of the pipe and how it's raised above the gasket and the edges are rough--doesn't look like the water will all drain out properly and will instead sit on top of the o'ring.