Bathrooms are on opposite ends of the house. Every now and then, both toilets will bubble/gurgle/splash when a bath tub is draining. Happens from either tub/shower draining.
Yesterday, this happened and the bathroom on the opposite end of the house from the draining tub had a bad sewer drain pipe smell right after.
I'm stumped as to what could cause such behavior. FYI - I'm on city sewer/water.
This is an indication that your Drainage has a `Fault`- sounds obvious - BUT this could be hard to `pin down` over this Forum - there will be many theory`s - as what you describe is caused by a Fault / Blockage [possibly partial blockage] that is causing `Negative Pressure` in your Drainage System.
NORMALLY we would be `diagnosing` that the `Venting` on your above ground drainage was `incorrect`- BUT you have stated that the `Toilets` are on opposite ends of the house - so it is very unlikely that you have all the `Toilets` and Baths etc. connected into the same above ground drainage - In the U.K. [where I am] - we call this - Soil Stack for W.C. [Toilet] Drainage and other waste water - OR Waste Water Stack for water only [+ condensate - if PVC] .
What does `Link` all your W.C. [Toilet] Drainage and All the Waste Water Drainage - including your Baths is the MAIN DRAIN RUN from your property - AND it `seems` that there `must be` an issue with `VENTING` that MAIN DRAIN RUN [?]
This is just ONE of the `Theories` that you will get regarding your `problem`-
You MAY have a `partial blockage` in a section of your main drain run - which does allow Water and some solids to pass - this could be `far enough` away from your property that no `back - up ` has reached the bathrooms etc - YET.
When you empty a Bath or have a `long` Shower- the Volume of water discharging into the DRAIN RUN and filling it up quicker than the `partial blockage` will allow the water to Drain away - causes a `Positive Pressure` - which has the W.C.`s [Toilets] to `Gurgle` - THEN as the Volume of water passes the `Partial Blockage` - a situation arises where a section of the Drain Run is FULL of water and is NOW `sucking` [Negative Pressure] the water out of the Bath Trap [and others?] - allowing the `Smell` and `Germs` from the Drainage System to enter your home.
Although the `Smell` is `distasteful` - these `Fumes` are Dangerous to your Health - Germs are coming into your property - VIA the `siphoned` Bath [and other] Trap which when empty - is the end of a direct pipe to the Sewers !!
You should Run a Bath Tap [Faucet] after you Drain the Bath - to FILL UP the trap again [ as a temporary measure] - which will `re-establish` the SEAL - and eliminate the `exit` of the `Smell`/ `Unhealthy Gases`.
What I have described can [usually] only happen when there is an `existing problem` with the `VENTING` of the DRAINAGE SYSTEM - and then a `Partial Blockage` occurs - EVEN THEN - the circumstances have to be `just right` - to cause the Problem that you seem to have.
It is not be possible to be SURE that this is DEFINITELY what is happening at your property - BUT I would recommend that you TRY to `check` your Drain Run - If you have Inspection Chambers / `Clean outs` ? - try to check using a FULL BATH of water -each time- IF the water is flowing away as fast - down the Drain Run - as it should be ? - Also note any `effect` that you notice on the `Traps` of Sinks, Baths, Basins, Bidets etc. - you already know that the `Gurgling` of the Toilets is happening - CHECK that this seems to be Air emitting FROM the Toilets ? - not a `Sucking` effect ? [Siphoning].
Although EITHER is indicating `Pressures` which should NOT be occurring in your Drainage/ Waste Water System - it might be `useful` to know WHICH is happening.[?]
The `issue` with the VENTING of the Drainage is that: the situation that I have described - SHOULD NOT BE ABLE TO HAPPEN.
The Drainage Runs should have `Stacks`/ Vent Pipes connected to them which would allow `Air Behind Water` - to prevent `Negative` and `Positive` Pressure Situations of the kind that I have described.
I await - `with interest`- the comments of the other `Professional Plumbers` regarding my descriptions here .
And of course there will be other `Theories` some of which may be just as `Valid` as this and some that may identify your problem `more correctly` ??
I am based in the U.K. - London - England - BUT these `unusual problems` can arise anywhere that there is Drainage.
As a `Postscript` - there could have been a `Problem` with the incorrect/ lack of VENTING to the Drain Run
which did not cause any problems [noticeable] - UNTIL `combined` with a `partial blockage`- for example an `undersized` vent - which allowed `Air behind Water` - UNTIL the `Pressures`- Negative and Positive were `created`- which `overcame` the inadequate Venting - and THEN the W.C.`s [Toilets] and the Bath Trap [and others?] were affected - `Gurgling` Toilets and `Siphoned` Bath Trap.
An example of `Inadequate Venting` would be where a `Soil Stack`[U.K.] - the Main 4" Down Pipe
for `Toilets`[ W.C`s] - which had 2 Toilet pans discharging into it - had a 2" Vent Pipe - COMPLETELY INCORRECT/INADEQUATE - when the Toilets were `flushed` the volume of water [etc] filling the Stack - flowing vertically - would Siphon water out of the `traps` on the Toilet Pans - because the 2" [inadequate] Vent would NOT allow enough AIR into the Stack to prevent the water being Siphoned out of the Toilet Pans, this would also be incorrect for a `Stack` with One Toilet Pan discharging into it !
If the `Venting` is inadequate - when `Positive`or `Negative` Pressures build - up / occur - they cannot be `relieved` / `negated` by the Vent - as the Pipe Diameter/ Volume cannot either allow enough AIR out of / into the Drainage/ Above ground Pipework.
This results in the type of problem that you are experiencing.
Your Drainage `Venting` might have been `Accidentally Adequate` - BUT `TOTALLY INCORRECT` - for the `Normal` discharging of Water and `Toilets` - so no problems were noticed - UNTIL combined with the `Partial Blockage` - WHEN the problem then `came to light` ??
I hope that I have not `worried` you too much - THIS is a good example of a `Problem` that needs the investigative knowledge of a `Professional Plumber` - who would investigate the `Venting Issue` and check the Drainage System for any obstruction / `partial blockage`.
I really do hope that you find a `Simple Fix` for this - BUT above is `MY Theory` - of a `situation` which CAN HAPPEN - I would be `VERY INTERESTED` in the Solution - after YOU or a `Professional Plumber` / `Drainage Expert`- have solved the problem - will you please `Post` the outcome here.
"Good Luck" CHRISM.