- 250 °C hotend
- 80 °C bed
- 0.15 mm first layer
- 0.2 mm layer height
- No Z-hop/retraction
- 40 mm/s print speed
- 50 % fan speed
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It looks to me like you're using Cura with the default Ender 3 custom start gcode. The priming line there tries to cram about twice the amount of filament through the nozzle as what it should, so unless your material and temperature can handle really fast flow, you'll build up pressure in the bowden, the retraction before the move to start printing will fail to actually back the filament out enough to stop flow, and you'll get a string. This will continue until sufficient oozing has happened to dump all the excess filament.
Going back and forth over the same line is also problematic, as it will pick up any blobs that got dropped off the first time over, melt them on the nozzle, and drag them into the print area. PETG really hates that. Whereas with PLA it just tends to leave the junk stuck to the model somewhere, with PETG it'll get dragged around and break things off the build plate or the model.
I replaced the priming part of the start gcode with:
G1 X0.1 Y20 Z0.3 F5000.0 ; Move to start position G1 X0.1 Y200.0 Z0.3 F750.0 E18 ; Draw the first line
Note that there is no second line.
I also reduced the final retraction in the end gcode from 3mm to 1mm so that the filament is left in a position where it doesn't require a lot of advancement to start priming, comparable to what you get after loading filament manually. Otherwise, you need extra priming at the start to make up for the difference, and then after loading new filament you'll over-extrude during priming.
Oh, you also need retraction, regardless of material. I missed that you had it off. Anyone telling you to turn off retraction for your general settings is wrong as that will always cause stringing; it's just a matter of how much1.
1 - see discussion in comments.