Septic vent?

Having dealt with slow toilets after heavy rains over the 25 years in this home, something came to me today. After heavy rains last nite, my sink was gurgling when I took my shower. Having company planned for the weekend, and it being several years since having the tank pumped anyway, I had the tank pumped to save the weekend. To my surprise, even though there was a good amount of sediment, the water level in the tank was at normal level( a foot or so down from top), so why were my sinks gurgling? Could it be that heavy rains seal the system so its harder for waste to go down? Could venting the septic tank help? Just wondered if anyone else had experienced this. Thanks for any input,,, Steve

A septic tank is already vented through the drain/waste/vent stack through the roof of your home.
The rain only has to do with soil saturation, which affects how fast the septic tank can drain liquid effluent into the drainfield in the ground. If the ground is saturated, it will make the septic tank sluggish, and possibly even cause it to back up (usually into a tub, the lowest drain point in the house, unless you have a basement).
You can add another drainfield line which will help allow the tank to drain faster. Septic tank drainage has to do with soil type that the drain field is in.
Consult your local Health Department for permit and inspection requirements.
Good Luck!
Mike