We live in a condo. Our kitchen sink will gurgle a lot. From time to time, there will be bubbles and even an overflow of bubbles and some sediment coming up from the kitchen drain. Someone has suggested that the problem is from the previous owner who relocated the kitchen sink and did not include the proper drop from the sink to the drain in the wall. Because there is a negative slope to the pipe, water cannot drain out of the pipe, the water gurgles and backs up. He has suggested that I need to re-do the drain system and have the water travel downhill at a sharper angle. I do not have a lot of money and would like to find another solution if it exists.
Since you already have a suspicion about the cause, the first step would be to confirm that. The drain should slope at a rate of 1/4" per foot. So if you had a 4' drain, there should be a difference of 1" in height between the start and end. If its negative then that's without a doubt the issue. If this is the cause, the only way to fix it is to re-plumb it. If you are handy, it is certainly doable.
If the slope isn't the issue then you have to start looking elsewhere. It is probably worth confirming that the trap is clear of obstructions. Remove the trap below the sink and clean it out.
If that fails then while it could still be a clog, its more likely a venting issue as BMitch suggested.
This isn't likely to be a big job for a plumber, so it might be most cost effective just to have one come out and do it right versus buying all the tools and parts needed.
Bubbles and gurgling typically indicate a problem with the vent in the plumbing line. Either the vent is blocked, improperly located, or not installed at all. Local building codes may allow you to fix this with an air admittance valve. But unless you know what you're doing, I'd suggest getting a licensed plumber in there to review this work and recommend the proper repair.
If the sink has been relocated the problem may also be distance of the sink from a main "vented drain" and or what the drain of the sink has been connected into. but as mentioned if you suspect the fall problem this would be the easiest to check also if this problem has just started does the sink have a removalbe trap that can be checked for blockages? have you checked the main drain for blockages?