18 is the base pressure / minimum pressure the car will run. The solenoid hoses are completely separate from the boost system.
If the wastegate lower nipple is hooked directly to the intake manifold then, in theory, it should peak right around 18psi. If you have a boost controller of some sort then that will increase your base pressure. The plausible causes:
1) boost solenoid or hoses were disturbed while doing working on the other hoses
2) if your boost solenoid or boost gauge tie into the intake manifold's front nipple then the readings 'could' change now that the hoses have been switched around, leading into #3
3) If the boost was set at 20psi using a boost controller and now runs 25psi after amending the hoses then there was most likely a boost leak where the purge valve attaches to the intake manifold since there are no barbs at either of those nipples.
If you have not already done so, put a zip tie on every hose that connects to the intake manifold as well as one at the BPV, wastegate, and boost controller.