I think I would have it pumped soon, if for no other reason, peace of mind. 17 years is a pretty long time, it doesn"t cost THAT much to have a tank pumped, and then you wouldn"t have to be concerned about it again for a long time.
If you know just where the septic tank is, it will probably save you quite a bit of money if you dig enough to be able to open the lids. Most septic tank pumpers will do the digging, but they sure don"t like it much and charge accordingly.
Most fairly modern tanks have two chambers, with the second chamber designed to catch any overflow of solids from the main chamber, rather than letting the solids pass out of the tank and plug up the drainfield. So you probably need to dig enough to open both large lids, so the pumper can empty both chambers. When I have had my septic tank pumped, usually about every 10 years, there was several feet of ashy looking solids in the main chamber, but almost nothing but liquid in the second chamber.
Have I ever had any problems with my septic tank or drainfield? No, but we do try to not add excessive solids to the tank and do have it pumped every few years.
It is a heck of a lot cheaper to have a septic tank pumped once in awhile than it is to have to replace a drainfield. And with the more recent regulations that have been passed in the 35 years since I put this system in, I might have to do a much more elaborate and expensive system. Those newer systems usually involve pressure mounds, electric pumps and lots more cost. My current system works by gravity, which is free and always there.
I would get the job done ASAP, and hope it is in time. Good luck!