There are a couple of different configurations, in one there is a bolt that mounts at the tube base to the pan right where the seal is, and there should also be a second bolt/flange about 1/2 to 2/3 of the way up to the dipstick end. The other configuration has two tabs bolted to the block split evenly in the mid section of the tube.
Get your finger behind the tube base against the engine and probe for a bolt that mounts into the oil pan top>down. Or use a mirror, this would need to be removed along with one more up towards the top holding the tube via a welded flange to the block.
If you dont feel a bolt at the base, then it is press fit into the seal, requiring you to unbolt it from the block via 1 or 2 flanges welded to the tube. Remove these bolts and withdraw the tube at its base upwards and out of the seal.