The general answer is that the showers and toilets can use the same drain, but they should not be sharing the same waste trap arm.
In most cases, shower water and toilet water do go to the same place, which is the sewer or septic system. In a typical plumbing system, all wastewater from the house is collected in a main sewer line and transported to a treatment plant or septic tank.
Toilet plumbing and sewage systems are more delicate than you think. Human waste and biodegradable toilet paper are the only things that should go down them. Anything else can cause major backups into things like your shower drain, which could make you think twice about hopping in to clean yourself up.
Your bathtub and toilet drain down separate pipes until they reach the main sewer line, which is the primary pipe to which all drains in your house lead. Eventually, all the drained materials mix and are forced out of your home through one line: the sewer main.
Sure. It creates another penetration in the roof, which I try hard to avoid, but in a house with a large footprint, it can save a long vent pipe run to take each bathroom and kitchen up through the roof without combining them. Or there's some open-ceiling design that precludes running them in an attic space to combine.
In your home plumbing system there is a plumbing fixture (like a toilet) that is supposed to be connected to a trap and each of these fixtures should have their own vent. What makes toilets unique is that they have a built-in trap, but, without a vent so you still need to install one for it.
Venting is necessary for bathroom plumbing systems to prevent blockage. All pipes in your home, particularly for toilets, sinks, and showers, require proper venting. It protects the trap on the drain pipe. In addition, it helps you secure your wallet, fittings, time, and even the pipe itself.
If your toilet is overflowing when you take a shower, there is an obstruction located between the toilet and the main sewer line. This is causing the water from the shower to back up and overflow at the first drain it reaches, which happens to be your toilet.
Note: If you see black gunk coming out of your drain, you may have a sewage blockage. Call a professional plumber for help, as this is a serious problem and can be a health issue. You'll probably also need professional help if multiple drains and toilets in your home are draining slowly or backing up.
When the shower and toilet are both clogged, the obstruction will likely be downstream from the area where the shower and toilet connect with the underlying sewer main. Such simultaneously clogging is a sign the obstruction is so deep that it backs up both drains.
P-Trap Shower Drain
Whether you have a standing shower or bathtub, it will always have a p-trap. The p-trap for showers is located underneath. Like the other fixtures, the shower drain p-trap prevents sewer odors from escaping your pipes.
Air Trapped in Vent
The pipes extend from the drain up through the roof, transferring wastewater and odour away from the house. Gurgling can occur if the vents become clogged. When air cannot escape through vents, it forces itself through the drains. The resulting difference in pressure causes gurgling.
According to regulations, all shower drains are required to have P-traps. This includes all fixtures connected to a building's main plumbing system. P-traps are curved pipes installed under showers and drains of all kinds.
Shower vs. Tub Drains. A shower uses a floor drain, which directly removes wastewater from the shower instantaneously as you bathe. A tub drain, on the other hand, needs you to manually close or open it with a lift-and-turn mechanism or a lever.
In a city, household drains connect to a larger pipe that carries wastewater into the city's underground collection system of sanitary sewers. As wastewater from homes, businesses and industries collects, sanitary sewer pipes get bigger and bigger as they near the wastewater plant.
If your shower drain stinks of sewage, it's an indication that your P-trap isn't effectively preventing sewer gases from leaking into your bathroom. If you're dealing with a mustier or general odor and your P-trap is still clogged, it's probably because it needs to be cleaned.
If the P-trap isn't working properly, sewer gasses can make their way into the bathroom and cause your sink to stink. Your sink should also have a vent that gives backflowing gases somewhere to go. If the sewer smell in your sink is caused by a blocked air vent, you may need professional assistance.
A rotten egg smell is caused either by biofilm clogging the shower drain or the backup of sewer gasses through the drain.
Here's the longer answer: Your shower and toilet most likely share a drain line and a vent stack (this setup is called wet venting, more on that later). If either the line or the stack has a clog or blockage, air is forced either up or down your toilet, making the gurgling noise you're hearing.
The most common configuration is to feed 2" PVC down from the ceiling within the wall behind the toilet. The vent pipe connects into the toilet drain pipe. The sink drain pipe and the tub/shower drain pipe are vented with 1.5" pipe that branches off from the 2" PVC mainline.
Poorly-vented drain lines will not be able to effectively move wastewater and solid waste out of your building. This could lead to problems such as overflowing drains, backed-up toilets, and similar plumbing issues.
Without a vent to allow pressure to escape from the plumbing system, harmful sewer gases can build up and make it difficult for water to move through the pipes efficiently.
Yes, plumbing vents can go out the wall instead of the roof. But both methods have their pros and cons that should be considered.
According to the UPC, the distance between your trap and the vent should be no more than 6 feet. In other words, for the vent to work properly, it needs to feed into the drain line within 6 feet of the trapways that connect to it.