Yep..you do need help!
That's probably a total newbie question, but then I AM a total newbie with this stuff. I've never had a boat with a holding tank before and there's no gauge and you can't see through the walls of the tank (thank goodness!).
So how can I tell when it's getting full and needs pumping out? Will the head just be too difficult to pump (grocco)? What happens? I don't even want to imagine overfilling and blowing something up! I don't know if there's an overflow or what (and where would an overflow go anyway?).Help! Dupree
If you cannot determine the level in the tank visually, CG regs require a gauge. You can buy a cheap one that only lets you know when the tank is full...or spend a bit more for one that tells how much is actually in the tank. I recommend that approach.
This one is your best choice...
http://ferriellosales.com/ A number of people here have 'em and will agree that it's an excellent product and that Dennis Fierello provides the best customer service and installation assistance on the planet. The price is very reasonable, and the product is reliable.
Yes, holding tanks do have a vent...a line coming off the top of the tank to a thru-hull fitting on the hull, prob'ly very close to the toe rail. It is an AIR vent line, NOT an overflow...allowing waste to overflow out the vent will cause it to become blocked, which can indeed result in a burst tank. Your first that the vent is blocked is a toilet that's becoming harder to pump, 'cuz that means the tank is becoming pressurized...so you want to cease using the toilet until the vent is clear again.
The link in my signature here will take you to a comprehensive "marine toilets and holding tanks 101" manual that should help you understand how to use and maintain your system to keep it trouble free. You'll also find a lot of info in the previous threads in this forum. And I'm here to answer questions too.
Btw...if I were you, I'd have the tank pumped out and also thoroughly rinse out the tank before you use the toilet again. Then, if you know how many gallons the tank holds, while you're waiting for the gauge to arrive via UPS, you can get a rough estimate of how many flushes using the following math:
On average, an adult uses the toilet 5x/24 hours...average flush volume: .6 gal. So each person continuously aboard will put approx. 3 gal./day into the tank..a couple will put 6 gals/day into it. So a 20 gal. tank should easily last 3 days without overflowing...a 12 gal tank barely a one-overnight weekend.
So it becomes obvious that you really do need to know how much is in the tank before you leave the marina...are you just one flush away from full, or only half a tank? A gauge that only tells you when the tank is full is legal, but otherwise useless.l.