no proper flow.partailly blocked pipes which fill up to capacity with shower water which eventually slowly drains; the flow from a flushing toilet after some time(you stated; 45 minutes) is simply because the shower wated has drained....clean the pipes check for roots from neighbouring trees/shrubs, remove ,seal the hole and the flow should normalise
Your drain line is plugged somewhere after your shower and toilet line are connected. The reason for the gurgle in your toilet is because air is trapped in the drain and your toilet is the closest place for air to flow to. If you had a vent on your toilet trap arm then it would gurgle in the vent rather in your toilet but your drain is still plugged and needs to be snaked out and maybe your drain line needs to be examined for right grade or broken.
When the toilet is flushed, it can create a sudden change in water pressure in the plumbing system. This change in pressure can cause air to be sucked into the pipes, leading to the gurgling sound in the shower drain.
When you flush the toilet, the sudden rush of water can create air bubbles in the plumbing system. These air bubbles can travel through the pipes and escape through the tub drain, causing the gurgling sound.
Because it effects the water pressure of the shower. This causes the temperature of the water in the shower to also change.
If it is full, you can't put more in it, full is full. Flush the toilet, it is going to come up in the shower. == == == == == ==
Supply and installation about -600.
When you shower, the water going down the drain can create a vacuum in the plumbing system, causing air to be pulled in through the toilet's trap, which results in the gurgling sound.
Probably because the line is still at least partially clogged.
The drain is plugged somewhat between the upstairs and downstairs. Need to snake the drains.
You can change the seals on your shower to ensure that you don't have a leak. You can also make sure that your fixtures are firmly attached to the shower head.
The drain from the toilet to the main drain is plugged and the branch to the shower is not. If the main floor toilet flushes, it is between the two toilets and not between the house and the sewer.